Not to mention the idea that she took away focus is honestly laughable. She has the least amount of screen time of the trio, she spends a good portion of the game asleep or off screen not really affecting anything.
Y'know, the first part about the screen time doesn't say much when 98% of the time she isn't around is still spent either
talking about her or following events/situations that still have
centrally to do with her, which makes the last bit almost laughable as Xion affected practically
everything throughout Days. Even things that are at first glance not about her in some way are eventually twisted around to do include her in some manner.
None of the characters had an agenda or scenario of his/her own that didn't involve Xion in some way, which is why I can understand Audo's assessment of Xion being the "black hole" of the story that draws everything in.
Because of this every statement about "just removing Xion is not enough" hits the bullseye. In order for Days to work without Xion the "one-woman-spotlight-stealing-squad" the structure of the narrative would also need quite some tweaking and/or rewriting by itself.
It would be immediately better.
But, frankly, the story of Days misses many opportunities so just "Days but Xion is gone" would still be a disappointment.
What Days needed to do was give Riku, DiZ, Mickey and Naminé larger roles. What are they doing for that whole year? What are the Organization doing in response?
The Days we got has us chase after "an imposter" but never once does the Organization endeavor to find out who the imposter is exactly and who he's working for, if anyone. It feels like a lazy way to get Riku into the story. But the rest of the crew don't even get that much. Mickey is in the game for one (1) scene. Why did he separate from Riku? What has he been doing?
How did DiZ transport Sora, Donald and Goofy from Castle Oblivion to Twilight Town? What happened inside the mansion that caused its destroyed appearance in KHII?
There are too many questions that still remain from that time period, too many lost opportunities for this or that character to have their time to shine; in my opinion, Days​ needs a complete rewrite.
Xion, from a narrative perspective, is literally Roxas.
The newest recruit in a shady organization, who searches for the truth behind the Keyblade and their own identity.
That she's a Replica almost feels like a cheeky way for them to say "yeah, we know." But that doesn't make it better. Even Riku Replica, who was a 1:1 copy, had a different character arc and place in the story from Riku.
Xion didn't need Roxas to pursue those answers for herself. Likewise, Roxas does not need Xion.
Besides that, Roxas was ostensibly a bystander for most of the story, with Xion progressing the narrative completely without his input or even knowledge.
Xion is entirely redundant as a character and as an addition to this narrative. She is the embodiment of filler.
It wouldn't be immediately better without further adjustments due to the structure of Days essentially having everything revolving around Xion as a central angle like planets resolve around a star.
Riku, DiZ, Mickey and Naminé not receiving more coverage during Days was partly also a consequence of this, because their bits couldn't be tied any closer to Xion without totally crashing the story, even more than it already was by canon Days.
It is somewhat irritating though I agree that the writers apparently had no idea/confidence to take up and build upon the open questions and possible exploration into other characters
that were already there and instead had to bring in an entirely "new" scenario which pushes everything else aside in favor for essentially repeating the Clone Conga/Riku Replica-story just with a different colorisation (a female this time, but has to be another Kairi-clone, and with camouflage powers due to yet more memory-shenanigans, yay) and instigating yet another rehash of the "main trio" dynamic which wasn't possible with already existing Naminé due to her not being with the Org and possible contradictions with already existing KH 2.
Heh, as far as I've observed many fans who dislike Roxas' portrayal in Days do so not because of the "Zombie-like" empty toddler-"personality" of the beginning parts (these are logical and consistent with Rox not having any memories to start with) but because this beginning characterisation does not evolve eventually into the investigative (and partly aggressive) characterisation Roxas was already known for.
There would have been hundreds of possibilities and opportunities for a more active and investigative Roxas to clash (mostly verbally and showing his more aggressive, forceful side) with
different Organisation members throughout the whole narrative in his quest for answers, with Axel probably then being the one he trusts the most to a certain extent.
Him eventually getting fed up and then after some especially big fallout (especially with Axel) finally deciding to leave completely could still have happened towards the end, possibly even due to subtle "propaganda" and nudging by "impostor" Riku from the sidelines or even Naminé (that Mickey was kept away from Roxas like 100% is reasonable due to the Ven issue. Had Mickey get to actually see or meet Roxas before Re: Coded, BBS-shenanigans would have been needed to address).
What people actually got though was indeed a "bystander"-Roxas who didn't really do anything beyond constantly whining about Xion as soon as she is introduced.
The few development and evolution Roxas actually does show and get towards his more independent mindset are all squeezed into the last five days or so like that one telling scene in Agrabah which got removed from the movie version, and they manage to make even
those somehow centered about Xion, including Deep Dive itself and the totally unneccessary bit of her being "present" in the Oblivion and asking Riku to do what he was about to do anyways.
Even in scenes and events where she isn't present you can make a drinking game out of betting how long it takes for the topic to swing being about her in some form.